1. Field of the Invention
The present invention relates to a circuit arrangement of a source current supply of a vehicle, in which the source voltage supply characteristics to the electronic equipment of reverse connection prevention type are improved especially at the time of the starting.
2. Description of the Prior Art
FIG. 1 shows one example of a conventional current supply circuit for vehicle electronic equipment of a reverse connection prevention type. In this figure, the reference numeral 1 designates positive (+) terminal of the battery, 2 an ignition switch, 3 an ignition relay, 4 an ignition line, 5 a diode for preventing reverse connection and 6 an electronic equipment comprising a constant voltage circuit. The electronic equipment may be, for instance, and electronic controlled fuel injection device having semiconductor elements, or a fully transistorized electric distributor circuit. Reference numeral 7 is a starter line.
This current supply circuit operates as follows. Namely, at the time of operation of the ignition relay 3 by the manual closure of the ignition switch 2, the contact 3a of the ignition relay becomes ON condition and the source voltage required for the operation of the electronic equipment 6 is supplied through the ignition line 4 and via a diode 5 coupled in the forward direction. In the drawing the reference numeral 4a designates an inductive load such as the alternator, the ignition coil, etc.
It has been the usual practice to insert the diode 5 for the protection of the electronic equipment having semiconductor parts. This is by a reason that an abnormally high reverse voltage might be induced at the time of switching off the ignition switch which results breakage of the semiconductor element. A same danger is expected by a mishandling to connect the battery terminal at reverse polarity.
In the aforementioned conventional current supply circuit for the electronic apparatus of a vehicle, the voltage to the electronic equipment 6 is supplied only through the ignition line 4 having the diode 5 inserted. This circuit arrangement has a disadvantage in that the supply voltage to the electronic equipment greatly decreases at the time of starting of the engine due to source voltage drop by the load such as the starter motor connected on the starter line 7 and also by the influence of the forward voltage drop of the diode 5. This decrease of the source supply voltage to the electronic equipment 6 may result unstable operation of the electronic equipment.